The invention relates to a capped electric lamp comprising:
a light-transmitting tubular lamp vessel which is sealed in a vacuumtight manner; PA1 an electric element inside the lamp vessel; PA1 a lamp cap provided with a projecting contact pin and fixed to the lamp vessel; and PA1 an electrical conductor connected to the electric element and to said contact pin.
The lamp cap has a housing of metal sheet which has a cylindrical shell and an axis, and integral therewith a base which is transverse to the axis and remote from the lamp vessel and which has an opening, in which base a cavity is formed in which an insulator plate is retained by a flanged portion in the housing so as to cover said opening, which insulator plate supports said contact pin such that said contact pin enters the opening.
Such an electric lamp is known from U.S. Pat. No. 2,457,789.
In the known lamp, the cavity in the base of the lamp cap shell is formed by depressing the base is locally inwards. After the insulator plate is introduced into the cavity from the outside, the plate fixed in the cavity by means of a flanged portion which is made in the base. The flanged portion makes the entrance of the cavity smaller and thus closes in the plate. The formation of the cavity has made the housing locally double-walled, which gives the housing a comparatively large material content.
The known lamp is a tubular fluorescent lamp which has two contact pins at its lamp cap. The pins must project from the base over a predetermined minimum length. The flanged portion which keeps the insulator plate in place has a thickness of twice the material thickness of the housing. The contact pins accordingly project less far from the base by said thickness than they do outside the insulator plate. They must be extra long to compensate for this. This is a disadvantage, the more so in the frequently used tubular fluorescent lamps which have two such lamp caps.